In the present well plugging technology, various forms of packer for specialized uses have been developed; they may be operated mechanically, hydraulically, hydro mechanically, or operated in a self-sealing manner. For example, in U.S. Pat. No. 6,073,692, a packer comprising a corrugated mandrel is disclosed, in which a mandrel swells as a fluid or mechanical force is applied, which leads to a change in the cross-sectional shape. In U.S. Pat. No. 4,886,117, the packer swells as pressure is accumulated down in the well, in between the inner and outer layers of elastomer, an intermediate sleeve formed of multiple plies of reinforcing strands are present. In U.S. Pat. No. 4,753,444, the annular seal of the packer comprises of poly arylene ketone and the like; the seal is buckled radically outwardly as it is compressed longitudinally, and thereby seals the packer. As described in U.S. Pat. No. 4,781,249, with the use of a valve device, a progressively swollen packer is achieved. In CN2242332Y, a packer comprising a concentric reducer, fluorine, and a lead-sealing ring is disclosed, in which sealing is made possible through the up and down movement of an oil tubing string. In CN2617919Y, the rubber packer swells as the metal jacket slides. In CN1236857A, plugging is achieved by the activation of a rubber packer caused by a water-based fluid under the action of a guilding device. As disclosed in CN2386189Y, the packer comprises an adapter, bushing, rubber packer and the like, in which plugging occurs after supplying water into the packer. Complicated structure constitutes a common disadvantage to the packers above.
To simplify the structure of a well packer, researchers, in recent years, are dedicated to study novel well packers. For example, in CN1452686A (WO 02/20941A1), a well packer is disclosed, in which sealing is achieved by the use of a swellable element fabricating of rubber, outer protecting jacket and reinforcement unit surrounding the swellable element. However, this patent application covers no rubber composition and the preparation thereof. It is well-known that most of the non-polar rubbers have an affinity for oily medium and possess oil absorption capacity. Rubbers of the same kind having different vulcanization components or prepared from different vulicanization process show very differently when they are put in the same solvent over the same period of time, in which some of them are soft and viscous while some of them just simply swell, and they are not reproducible. In addition, both of outer protecting jacket and reinforcement unit are used in this technology, and thus the structure of such packer is relatively complicated.
It is obvious that improvements of the swelling speed and rate of the oil absorbing rubber or the oil absorbing and water absorbing rubber, as well as fulfillment of the harsh condition required down in the well are important for the achievement of the technology in preparing such well packer using the swellable rubber, which represent a problem urgently required to be addressed in the art.
To overcome the above problems, one technical approach is to introduce lipophilic groups into the rubber, which results in the formation of a superior oil swellable rubber. To increase the amount of lipophilic groups in the rubber, two approaches are proposed. One approach is achieved by grafting lipophilic groups to the rubber, which is relatively complicated and the implementation is difficult, thus reports concerning such process have not been found. The other approach is to introduce high oil absorbing resin in the vulcanizing formulation for rubber through blending with rubber by physical blending, which results in the improvement of oil absorbing capacity and swelling capacity. This method is simple, but has a drawback of being difficult to obtain a homogenous dispersion of the 3-dimensional network structure of oil absorbing resin in the rubber matrix.
The inventor of the present invention has developed a new technical approach for preparing a superior oil swellable material, i.e., designing and synthesizing a starch-(meth)acrylate graft copolymer which is lipophilic and capable of improving the swelling speed and rate of oil absorbing materials containing rubber, and which can be effectively used as a swelling agent for the oil swellable material. Moreover, the inventor of the present invention further developed a new oil swellable material, in which the above starch-(meth)acrylate graft copolymer is used as the swelling agent, resulting in a great improvement in oil absorbing capacity and swelling capacity of the current materials, such as rubber. Soil swellable materialealing articles, particularly the well packers, can be made by using above oil swellable material. Since the rubber maintains a certain extent of mechanical strength, requirements for sealing the annular space between the mandrel and the jacket or the well wall could be satisfied. Also, the inventor of the present invention has designed and synthesized oil- and water-swellable materials, as well as sealing articles prepared from the same, particularly well packers.